MOUNTAIN COLLAPSE, UNDER THE SEA, TSUNAMI?

As the most active volcano in Europe, Mount Etna is intensively monitored by Italian scientists and authorities. Satellite-based measurements show that the southeastern side of the volcano is slowly moving towards the sea, while other slopes are mostly stable. Until now, it is not fully known whether and how the movement continues under water, because satellite-based measurements are not possible under the surface of the ocean. With the new GeoSEA basic geodetic monitoring network, scientists from the Helmholtz Center for GEOMAR Kiel Marine Research, Kiel University, Kiel Marine Science’s priority research fields, and the Istituto Nazionale in Geofisica e Vulcanologia (INGV) can now detect horizontal and vertical movements from the wing of a sinking volcano.

The results confirm that the entire southeast wing is moving. The driving force of wing movement is likely to be gravity, and not the rise of magma, as previously assumed. Severe collapse involving all wings or large parts of it cannot be ruled out and will trigger a large tsunami with extreme effects in the region. The results of the study have been published today in the journal Science Advances.

Pic. 1. Simulation of Fault displacement at Mount Etna from April 2016 to July 2017

“On Mount Etna we use a voice-based underwater geodetic monitoring network, called marine geodesy, in the volcano for the first time,” said Dr. Morelia Urlaub, lead author of this study. He led the investigation as part of the project “MAGOMET – marine geodesy for offshore monitoring of Mount Etna”. In April 2016, the GEOMAR team placed a total of five transponder stations on acoustic monitoring along the fault line which represented the boundary between the sliding side and a stable slope. “We put three in the sliding sector and two on the side that might be stable from the fault line,” said Dr Urlaub.

Pic. 2. Faults movements around Mount Etna

During the mission, each transponder sends an acoustic signal every 90 minutes. Because the speed of sound in water is known, the travel time between transponders signals information about the distance between transponders on the seabed with an accuracy of less than one centimeter. “We saw that in May 2017 the distance between transponders on various fault sides was clearly changing. The side slipped four centimeters towards the sea and eased by one centimeter in eight days,” explained Dr. Urlaub. This movement can be compared to very slow earthquakes, called “slow events.” This is the first time the horizontal movement of a slow slip event like that is recorded under water. In total, the system sends data for about 15 months.